Yes, pa is a Scrabble word!
...and is worth 4 points in Scrabble, and 5 points in Words with Friends
pa
Noun
1. An informal term for a father; probably derived from baby talk
2. A short-lived radioactive metallic element formed from uranium and disintegrating into actinium and then into lead
3. A unit of pressure equal to one newton per square meter
4. A Mid-Atlantic state; one of the original 13 colonies
5. An electronic amplification system used as a communication system in public areas